FR2712442A1 - Integrated transmission line coupler for radio frequency signal amplifiers. - Google Patents

Abstract

Transmission line coupler (115) for a transmit output signal (123) generated by an RF signal amplifier (103) comprising a direct path transmission line (201) and a coupled path transmission line (202 ) electromagnetically coupled to the first by multiple sinuous-shaped parts (such as parts 641, 642, 643 and 644 of Figure 6), which are disposed on opposite sides of the direct path transmission line (201) for increase the coupling sensitivity and eliminate any degradation of the coupling value as a result of variations in the etching of the transmission lines. The offset portions (641, 643) on one side of the direct path transmission line (201) provide substantially the same amount of coupling as the offset portions (642, 643) on the other side of the transmission line. direct path (201).

Description

INTEGRATED TRANSMISSION LINE COUPLER FOR

  RADIO FREQUENCY SIGNAL AMPLIFIERS

  Technical Field of the Invention The present invention generally relates to radio frequency (RF) signal couplers, and more particularly, to an integrated transmission line coupler for RF signal amplifiers.

  for cell phones.

  In conventional cellular telephones, RF signal couplers have been installed according to several methods, in particular by means of capacitive couplers or transmission line couplers. Previous transmission line couplers have generally been designed to close on loads of fifty ohms at all of their ports. Consequently, it is necessary to include a circuit at the output of an RF signal amplifier which allows the load to be adapted to fifty ohms. This output matching circuit usually comprises one or more transmission lines and several capacitors, resistors and / or inductors, elements which all require significant space for the circuits. In addition, the total insertion loss between the RF signal amplifier and the antenna involves losses due to both the output matching circuit and the transmission line coupler. For the above reasons, there is a need for a transmission line coupler integrated in the adaptation circuit of

  RF signal amplifier output.

Brief description of the drawings

  FIG. 1 is a simplified diagram of an RF transmitter circuit 100, which can be advantageously used by

the present invention.

  Figure 2 is a simplified diagram of a telephone

  cell 200 comprising the RF transmitter circuit 100.

  FIG. 3 is a detailed circuit diagram of the amplifier 103 and the detection circuit of

power 109 of figure 1.

  Figure 4 is a section of part of the transmitter circuit of Figure 1, showing the coupler

transmission lines 115.

  Figure 5 is a top view of the upper layer 321 of the circuit section of Figure 4, illustrating an embodiment of the transmission lines 201 and 202 of the line coupler

transmission 115.

  Figure 6 is a top view of the upper layer 321 of the circuit section of Figure 4, illustrating the preferred embodiment of the transmission lines 201 and 202 of the line coupler

transmission 115.

  FIG. 7 is a view from above of the upper layer 321 of the section of the circuit of FIG. 4, illustrating another embodiment of the transmission lines 201 and 202 of the transmission line coupler 115.

  Description of the preferred embodiment

  Briefly described, the present invention relates to an RF signal coupler circuit for detecting an RF signal generated by an amplifier and producing an RF detection signal. The amplifier also has an output coupled to the adaptation circuit of the transmission lines. The RF signal coupler circuit includes a substrate having upper and lower surfaces and a predetermined dielectric constant; a direct path transmission line having a predetermined shape and being arranged on the upper surface of the substrate, the direct path transmission line coupled to the RF signal and included in the circuit for adapting the transmission lines; and a coupled path transmission line being disposed on the bottom surface of the substrate and having a coupled port, coupled to a first complex impedance, and an isolated port coupled to a second complex impedance, the coupled path transmission line, electromagnetically to the direct path transmission line, to generate the RF detection signal at the coupled port having an amplitude related to the amplitude

of the RF signal.

  Referring to Figure 1, there is shown a simplified diagram of a single RF transmitter circuit 100, which can advantageously be used by the present invention. The RF transmitter circuit 100 is part of the cellular telephone 200 of FIG. 2, which also includes the receiver circuit 141, the user interface circuit 151 coupled to a microphone 152, to a speaker 153, and to a keyboard 154, all these elements being controlled by the microcomputer 111, elements which can compose any conventional cellular telephone, such as, for example, the cellular telephone illustrated and described in the Motorola Instruction Manual, number 68P81066E40, entitled "Transceiver 800 MHz for DYNATAC "cellular mobile phone, published and distributed by Motorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Illinois 60196. The operation and characteristics of this classic phone are described in the Motorola User Manual, number 68P81116258 , entitled "USER MANUAL for the DYNATAC 6800XL Cellular Mobile Phone", published and distributed by Motorola C & E Parts, 1313 East Alg onquin Road, Schaumburg,

Illinois 60196.

  The RF transmitter circuit 100 of FIG. 1 comprises cascade amplifiers 101, 102, and 103 coupled by the directional coupler 115 and the filter 105 at the antenna.

  107. The RF 100 transmitter circuit, as well as the micro-

  computer 111 and the receiver 141 of FIG. 2, can all be mounted on a multilayer printed circuit. The directional coupler 115 is preferably a coupler

  directional transmission lines, as described above

  below, and is coupled to the power detection circuit 109, which produces the power detection signal 131. The microcomputer 111 responds to the power detection signal 131 to adjust the value of the gain control signal 132 to produce level

  desired power of the output signal from the transmitter 123.

  The gain adjustment signal 132 is coupled to the control circuit 113 (which can be mounted as shown and described in US Patent No. 4,523,155 incorporated herein for reference) to adjust the voltage / current control of the amplifier 102, and therefore the gain in amplification thereof. In analog cell phones, the transmitter output signal 123 can be set to one of eight possible power levels in response to the command message from cellular base stations (see US Patent No. 4,523,155). In digital cellular telephones, the transmitter output signal 123 can be set to one of eight possible power levels during a defined time interval, in response to the command message from cellular base stations (see US Patent No. 5,192 .223, incorporated here for reference). Analog and digital cell phones can

  advantageously use the present invention.

  Referring to Figure 3, there is shown a detailed circuit diagram of the output amplifier 103 and the power detection circuit 109 of Figure 1. The amplifier 103 is preferably a transistor effect field (OKI type KGF1321S TEF) which is coupled to the amplified emission signal 122 by a capacitor and the transmission line 203 and generates the emission output signal 123. The output adaptation of the amplifier 103 comprises two sections low pass and an adaptation of harmonics for the second and third harmonics. The adaptation of harmonics is carried out by the transmission line 204 and the capacitor 243. The transmission line 205 and the

  capacitor 245 constitute a pass filter section

  bottom, and transmission line 201 and capacitor 247 constitute the other low pass filter section. The transmission line 201 is also coupled to the filter, which, in turn, is coupled by two capacitors and

an inductor at the antenna 107.

  According to a new characteristic of the present invention, the transmission lines 201 and 203 are integrated in the output adaptation of the amplifier 103. Since the coupler 115 is integrated in the output adaptation of the amplifier 103, the impedances complex to the coupled port and its isolated port of the transmission line with coupled path 202 (end connected to the inductor 210) must be carefully selected so that the signal appearing at the coupled port of the transmission line with coupled path 202 ( end connected to the inductor 212) comprises signals which circulate only in the conducting direction and does not include signals which circulate in the opposite direction. In conventional directional couplers, the direct path transmission line and the coupled path transmission line are designed to accept fifty ohms at all of their ports. In the ideal case where the line outputs have impedances of fifty ohms, part of the RF signal appears at the coupled port of the transmission line with coupled path, and no signal appears at the isolated port of the transmission line with path coupled. Likewise, no reflection of the signal Rf occurs since the two ports of the direct trajectory transmission line close ideally on impedances of fifty ohms. However, since the direct path transmission line 201 of the integrated coupler does not ideally end, but is on the contrary coupled between the capacitors 245 and 247, several reflections of the emission output signal 123 occur. In the coupler 115, a desired part of the transmit output signal 123 is coupled to the coupled port of the coupled path transmission line 202. The transmit output signal 123 descends to the transmission line 201 and a portion is reflected by the capacitor 247. The first reflected emission output signal returns and a portion is reflected by the capacitor 245. An unwanted portion of the second reflected emission output signal 123 is coupled to the coupled port of the transmission line to coupled path 202. A portion of the first reflected emission output signal 123 is also coupled to the isolated port of the coupled path transmission line 202 and returns to the coupled port of the coupled path transmission line 202. According to a new characteristic of the present invention, if the correct complex impedance of the isolated port appears at the isolated port of the transmission line through coupled ectory 202, the part of the first reflected emission signal 123 which returns to the coupled port cancels the coupled part of the second reflected emission signal 123. This correct complex impedance of the isolated port comprises a real part and an imaginary part , which is applied in the preferred embodiment by inductor 210 (15 nH) and resistor 222 (39 ohms) coupled in series to the isolated port of the coupled path transmission line 202. Using the correct complex impedance from the isolated port to cancel the unwanted parts of the reflected signals, the coupler 115 can be integrated into the output adaptation of the amplifier 103, which leads to significant savings, both in terms of

  circuit space and number of components.

  The correct complex impedance of the coupled port further increases the desired cancellation, and is applied in the preferred embodiment by the inductor 212 (5 nH) coupled in series with the inductor 211 (22 nH) and the resistance of the diode 206 of the coupled port of the transmission line to

coupled trajectory 202.

  The transmission line 201 provides a direct path for the transmit output signal 123. The coupled path transmission line 202 is electromagnetically coupled to the transmission line 201 to generate an RF detection signal having an amplitude related to the amplitude of the emission output signal 123. The RF detection signal of the transmission line 202 is coupled by the inductors 212 and 211 to the diode 206, which, with the capacitor 231, rectifies it in single phase to generate a DC voltage corresponding proportional which is stored on the

capacitor 231.

  The DC voltage stored on the capacitor 231 is coupled by the resistors 232-235 and the capacitor 236 to produce the power detection signal 131. The resistor 224 and the diode 207 generate a bias voltage from the voltage V2 which is coupled by the resistors 223 and 222 and the inductor 210 to the transmission line 202 to polarize the diode 206 by the inductors 212 and 211. The diodes 207 and 206 are preferably hot-carrier diodes having essentially the same characteristics electrical, such as, for example, Motorola diodes type MMBD770T1. The temperature of the diode 207 balances the diode 206 so that the power detection signal 131 does not fluctuate with variations in temperature. According to a new feature of the power detection circuit 109, an impedance applied as an inductor 211 (22 nH) is coupled to the diode 206 to adapt the resistance and the capacitance (1.5 pF) inherent in the diode, thereby improving the sensitivity of the power detection circuit 109 by a factor of two. Although applied with the inductor 211, the matching impedance can also be applied by the corresponding capacitive circuit. The matching impedance optimizes the power transmission to the diode 206 and is preferably optimized to operate at low power levels (for example, at power levels lower than one of the eight predetermined power levels possible), where sensitivity is very important. Since the power detection circuit 109 is more sensitive, the detection requires less signal and a coupler 115 with a 20 dB coupling can be used instead of the 15 dB coupling used in the detector circuits without inductor 211. The coupler with a 20 dB coupling reduces the insertion loss by about 0.1 dB, which translates into consumption savings of around 8 mA, extending

  thus notably the duration of emission of the battery.

  Referring to Figure 4, there is shown a part of the transmitter circuit 100 of Figure 1, which represents the coupler of transmission lines 115. The transmitter circuit 100 is mounted on a multilayer circuit or on a substrate having three layers of substrate, 321, 322 and 323, which in the preferred embodiment incorporate FR-4 fiberglass material having a dielectric constant of 4.66. The material of the substrate can also be any other suitable material, such as, for example, alumina, duroid, and quartz. Layer 321 comprises the direct path transmission line 201 made of metallized conductive material on its upper surface 301, and the coupled path transmission line 202 made of metallized conductive material on its lower surface 302. Another form of circuit metallization (not shown) can be included on other parts of the upper and lower surfaces 301 and 302 of the layer 321 of the circuit. Layer 322 is an intermediate layer which does not have circuit metallization. Layer 323 has a base metallization on its upper surface 303 providing a base for transmission lines 201 and 202, and another for metallization

  circuit (not shown) on its lower surface 304.

  Layers 321, 322 and 323 are metallized with the corresponding circuit and welded by lamination or other suitable methods to form

a circuit.

  Referring to Figure 5, there is shown a top view of the upper layer 321 of the circuit section of Figure 4, which illustrates an embodiment of the transmission lines 201 and 202 of the coupler of the transmission lines 115. According to a new characteristic of the coupler of the transmission lines 115, the transmission line 202 has a sinuous shape, as the parts 341, 342, and the parts 343, 344 are located on the opposite side of the transmission line 201, for a observer placed above,

as in figure 5.

  The transmission line coupler 115 is preferably sensitive enough to detect the low levels of the transmit output signal 123, and also has a relatively small loss to avoid unnecessary attenuation of the transmit output signal 123 and a excessive corresponding current consumption of the battery. By using the transmission line coupler 115, the electromagnetic coupling of 20 dB can be obtained in the frequency band 825 to 925 mHz with an insertion loss

less than 0.15 dB.

  The value of the electromagnetic coupling between the transmission line 201 and the transmission line 202 depends on the number of factors, including the width of the transmission line 202, the thickness of the layer 321, and the remote parts 341, 342, 343 and 344 are offset from the edges of line 201, and parallel to them. The parts 341, 342, 343 and 344 of FIG. 5 have a width less than the width of the transmission line 201, and are offset from the edges of the transmission line 201 by a substantially identical value. The length of the parts 341 and 342 taken together is substantially identical to the length of the parts 343 and 344 taken together. The coupling provided by the parts 341 and 342 taken together is substantially identical to the coupling provided by the parts 343 and 344 taken together. The electromagnetic coupling between the transmission line 201 and the transmission line 202 is maximum between the transmission line 201 and the parts 341, 342, 343 and 344, and minimum between the transmission line 201 and the perpendicular parts which pass under the transmission line 201. Consequently, small variations in etching between the circuit metallization on the upper surface 301 and the circuit metallization on the lower surface 302 of the layer 321, do not degrade the overall electromagnetic coupling between the transmission line 201 and the transmission line 202, since the coupling of the parts 341, 342 increases when the coupling of the parts 343, 344 decreases, and vice versa. Many other configurations and shapes of the transmission line 202 are possible, namely, the sawtooth, semi-circular, and elliptical configurations, as well as the configurations of Figures 6 and

7 described below.

  Referring to Figure 6, there is shown a top view of the upper layer 321 of the circuit section of Figure 4, which shows the preferred embodiment of the transmission lines 201 and 202 of the line coupler transmission 115. The transmission line 201 has a U-shape and the transmission line 202 comprises the parts 641 and 642, which are electromagnetically coupled to the parallel sides of the U-shaped transmission line 201, and the parts 643 and 644 which are coupled to the central side of the U-shaped transmission line 201. The parts 641, 642, 643 and 644 are spaced approximately 0.004 inch from the transmission line 201. The parts 641 and 642 are substantially the same length , and the parts 643 and 644 have substantially the same length. The total length of parts 641, 642, 643 and 644 taken together is approximately 0.4 inches. The coupling provided by part 641 is substantially identical to the coupling provided by part 642, and the coupling provided by part 643 is substantially identical to the coupling provided by part 644. Parts 641 and 644 provide at least 23 dB coupling , to produce an electromagnetic coupling of at least 20 dB in the frequency band 825 to 925 mHz with an insertion loss less than 0.15 dB. In this embodiment of FIG. 6, small variations in etching between the circuit metallization on the upper surface 301 and the circuit metallization on the lower surface 302 of the layer 321, can occur in the X and Y directions without degrading the overall coupling between the transmission line

  201 and the transmission line 202.

  Referring to Figure 7, there is shown a top view of the upper layer 321 of the circuit section of Figure 4, which shows another embodiment of the transmission lines 201 and 202 of the line coupler transmission 115. The transmission line 202 comprises parallel parts 741 and 742 which are parallel to the transmission line 201 and are electromagnetically coupled thereto. The parts 741 and 742 have substantially the same length, and the coupling provided by the parts 741 and 742 is substantially identical. In summary, a single transmission line coupler 115 includes a direct path transmission line 201 and a coupled path transmission line 202, which are embedded in the output matching of amplifier 103. The transmission line 201 acts as a low-pass filter section of the output adaptation of amplifier 103, and also serves as a direct path transmission line of coupler 115, which allows significant savings, both in terms of space of circuits and number of components, and reduces the loss

  by total insertion in the path between the amplifier 103 and the antenna 107.

Claims (8)

Claims   1. Radio frequency signal (RF) coupler circuit for detecting an RF signal generated by an amplifier and producing an RF detection signal, said amplifier having an output coupled to a circuit for adapting transmission lines, said coupler circuit comprising: a substrate having upper and lower surfaces and a predetermined dielectric constant; a direct trajectory transmission line having a predetermined shape and being arranged on the upper surface of the substrate, the direct trajectory transmission line being coupled to the RF signal and integrated in the circuit for adapting the transmission lines of the amplifier, and characterized in that: a transmission line with coupled path is arranged on the lower surface of the substrate and that it has a coupled port, coupled to a first complex impedance, and an isolated port coupled to a second complex impedance, the line path transmission system being electromagnetically coupled to the direct path transmission line to generate the RF detection signal at the coupled port having an amplitude related to the amplitude of the RF signal.   2. RF signal coupler circuit according to claim 1, characterized in that the transmission line adaptation circuit comprises a first low-pass filter section and a second low-pass filter section coupled in series at the output of the amplifier, and that the direct path transmission line is included in the second low-pass filter section of the transmission line adaptation circuit. A transmit circuit for amplifying a radio frequency (RF) signal and producing a transmit output signal at a predetermined power level, said transmit circuit comprising: a signal source for generating the RF signal; an amplifier coupled to the information signal and a gain control signal for amplifying the information signal by a variable gain to produce the transmit output signal, the variable gain being related to the value of the control signal gain, the amplifier having an output coupled to the transmission line matching circuit; a transmission line coupler coupled to the amplifier for generating an RF detection signal having an amplitude related to the amplitude of the transmission output signal, said transmission line coupler further comprising: a substrate having upper and lower surfaces and a predetermined dielectric constant; a direct trajectory transmission line having a predetermined shape and being disposed on the upper surface of the substrate, said direct trajectory transmission line being coupled to the RF signal and integrated in the circuit for adapting the transmission lines of the amplifier, and characterized in that: a transmission line with coupled path is arranged on the lower surface of the substrate and that it has a coupled port, coupled to a first complex impedance, and an isolated port coupled to a second complex impedance, the line coupled path transmission being electromagnetically coupled to the direct path transmission line to generate the RF detection signal at the coupled port having an amplitude related to the amplitude of the RF signal; and a control circuit coupled to the RF detection signal for adjusting the value of the gain adjustment signal to maintain the transmit output signal at the level of predetermined power.   4. Transmission circuit according to claim 3, characterized in that the control circuit further comprises a diode detector coupled by an inductor to the RF detection signal to rectify the RF detection signal in order to produce a signal of detection, said control circuit being coupled to the detection signal to adjust the value of the gain adjustment signal to maintain the transmission output signal at   predetermined power level.   5. Transmission circuit according to claim 3, characterized in that the circuit for adapting the transmission lines comprises a first band-pass filter section and a second band-pass filter section coupled in series to the output of the amplifier. , and in that the direct path transmission line is integrated in the second bandpass filter section of the   transmission line adaptation circuit.   6. In a cellular telephone, a transmit circuit for amplifying a radio frequency (RF) signal and producing a transmit output signal at a predetermined power level, said transmit circuit comprising: a signal source for generating the signal RF; an amplifier coupled to the information signal and a gain control signal for amplifying the information signal by a variable gain to produce the transmit output signal, the variable gain being related to the value of the control signal gain, the amplifier having an output coupled to the transmission line matching circuit; a transmission line coupler coupled to the amplifier for generating an RF detection signal having an amplitude related to the amplitude of the transmission output signal, said transmission line coupler further comprising: a substrate having upper and lower surfaces and a predetermined dielectric constant; a direct trajectory transmission line having a predetermined shape and being disposed on the upper surface of the substrate, said direct trajectory transmission line being coupled to the RF signal and integrated in the circuit for adapting the transmission lines of the amplifier, and characterized in that: a transmission line with coupled path is arranged on the lower surface of the substrate and that it has a coupled port, coupled to a first complex impedance, and an isolated port coupled to a second complex impedance, the line coupled path transmission being electromagnetically coupled to the direct path transmission line to generate the RF detection signal at the coupled port having an amplitude related to the amplitude of the RF signal; and a control circuit coupled to the RF detection signal for adjusting the value of the gain adjustment signal to maintain the transmit output signal at the predetermined power level; and an antenna coupled to the line coupler   transmission to transmit the transmit output signal.   7. Transmission circuit according to claim 6, characterized in that the control circuit further comprises a diode detector coupled by an inductor to the RF detection signal to rectify the RF detection signal in order to produce a signal of detection, said control circuit being coupled to the detection signal to adjust the value of the gain adjustment signal to maintain the transmission output signal at   predetermined power level.   8. Transmission circuit according to claim 6, characterized in that the transmission line adaptation circuit comprises a first band-pass filter section and a second band-pass filter section coupled in series to the output of the amplifier. , and in that the direct path transmission line is integrated in the second bandpass filter section of the   transmission line adaptation circuit.